How long does coffee keep you awake?

People have been enjoying caffeine, a naturally occurring substance found in some plants, for more than 10,000 years. It can be found in over 60 plants including tea leaves, cacao pods, and coffee beans.

Today, caffeine is also synthetically produced and added to a variety of medicines and foods. With it being such a prevalent ingredient in today’s world, there have been studies and research conducted on how it relates to our lives and the potential side effects it has. One particularly hot topic is the relationship between caffeine and sleep. In fact, studies have suggested that ingesting more than 400 mg of caffeine a day can negatively impact one’s ability to sleep among a long list of other negative side effects. So, if you reach for a cup of coffee right after supper, how long will it keep you up at night? Unfortunately, the truth is buried underneath several factors that can vary from person to person.

What’s Caffeine?

Simply stated, caffeine is a mild stimulant that affects the nervous system in our bodies. Consuming caffeine, a white powder that harbors a bitter taste, helps boost energy levels and alertness.

When consumed, it’s absorbed into the body in 45 minutes or less. If consumed on an empty stomach, 

it can reach peak levels in our blood in as little as 15 minutes. The energy-boosting effects can also be felt sooner in the brain. If caffeine is consumed with a meal or even after a meal, it can take 2 hours for the caffeine to peak in one’s system.

Where’s the Caffeine?

Caffeine can be found in a wide variety of food, drinks, and medicine today. Some of these caffeinated options include:

  • Coffee- on average, a serving of coffee contains 100 mg of caffeine
  • Espresso– one shot has approximately 64 mg of caffeine
  • Tea- the caffeine in black tea typically ranges from 40 to 120 mg per serving
  • Soda- has approximately 22 mg of caffeine
  • Chocolate- 1 oz of unsweetened baking chocolate contains roughly 23 mg of caffeine
  • Energy drinks- have close to 72 mg of caffeine
  • Multivitamins- one dose can have close to 210 mg of caffeine
  • Medicine- Excedrin Extra Strength pain medication has approximately 130 mg of caffeine per dose

Processing Caffeine

Ultimately, caffeine is broken down in the liver. With that being said, it also passes through the stomach, small intestines, and bloodstream. From the bloodstream, it invigorates the body’s nerves, brain, and spinal cord.


There are several factors that can affect how long caffeine stays in our bodies. This, in turn, plays a role in the difficulty one might have falling asleep. 

According to the FDA, the half-life of caffeine is between four and six hours. Essentially, six hours after drinking a cup of coffee, half of the caffeine content is still present in your body. 

With a half-life of four to six hours, caffeine can stay in your system for close to ten hours. In other words, it can keep you up for a while before fully exiting your bloodstream, thus delaying your bedtime.

How Does Caffeine Affect Sleep?

When ingested, caffeine blocks adenosine, a crucial hormone responsible for deep sleep. It also decreases the levels of other hormones, like melatonin and serotonin, which are all responsible and necessary for falling asleep.

Therefore, unless you have built up a caffeine tolerance or are a person who requires caffeine to help you fall asleep, it’s not suggested to drink coffee or other caffeinated beverages in the evening hours leading to bedtime.

Important Factors

As research continues, there are many areas that are still being studied in relation to how caffeine is metabolized. One factor that causes caffeine to break down more quickly is smoking. On the other hand, people who are pregnant or on birth control will face a longer time for their body to break down the caffeine.

Some other potentials factors to consider when trying to figure out if your evening “cup of joe” will keep you awake include:

  • Gender- caffeeine is metabolized at a slower rate in women and at a higher rate in men
  • Age- some research suggests older people may take longer to metabolize caffeine
  • Additives- dairy may slow down the rate of caffeine absorption in the body
  • Genetics- some people’s bodies are better at metabolizing caffeine than others
  • Diet- how much caffeine has already been consumed throughout the day
  • Time- 3:00 pm is the latest time suggested before stopping all daily caffeine consumption
  • Tolerance- daily consumption means the effects of caffeine won’t be as great

Too Much Caffeine

The FDA suggests that adults consume no more than 400 mg of caffeine per day, and if pregnant, you should consume no more than 200 mg per day. A good rule of thumb is to keep the daily caffeine intake between 200 mg and 300 mg.

Ingesting more than the daily recommended amount of caffeine can potentially cause some side effects. On top of insomnia, it may also increase one’s chances of:

  • Anxiety and increased heart rate
  • Headaches
  • Bladder control and frequent bathroom breaks
  • Irritability
  • Nervousness and jitters

Final Thoughts

There are several factors to consider when trying to answer the question of how long your cup of coffee will keep you awake. Everything from your gender, age, tolerance level, and genetics plays a role. Not only that, but environmental factors, like the time of day, how much caffeine has already been ingested, and what’s been added to the coffee can also contribute to the overall answer to that question.

To be on the safe side, stick to the daily recommended amount of caffeine and don’t ingest any after 3:00 pm. Even though it may be hard, especially when it comes to a fresh cup of coffee, your body will thank you at bedtime. Not only that, but then you will be less likely to experience side effects from over-caffeinating yourself.